Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2000-03-08
2003-02-18
Crispino, Richard (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S229000, C156S306300, C156S310000, C427S008000, C427S146000
Reexamination Certificate
active
06521066
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for producing a film sheet having at least one print carrier layer of plastic, an adhesive layer and a cover layer, the adhesive layer being applied to the print carrier layer, the print carrier layer provided with the adhesive layer being sent for drying and the print carrier layer provided with the adhesive layer after drying being combined with the cover layer to produce the film sheet. Furthermore the invention relates to an apparatus for performing the process.
2. Description of Related Art
In a known process for producing a film sheet, which is conventionally called a transfer process, the adhesive is applied to the cover layer which is coated with an adhesive-repellant silicone layer. Then, the silicone-treated cover layer with the applied adhesive is sent to a drying station so that the adhesive on the cover layer dries. Parallel thereto and subsequently, a so-called primer is applied to the plastic print carrier layer, and then, the print carrier layer provided with the primer and the cover layer with the applied adhesive are combined into the film sheet.
However, the above described transfer process has various disadvantages. With respect to the surface tension of the adhesive, wetting faults can occur upon application to the adhesive-repellant silicone layer. To preclude these wetting faults in the application of the adhesive, appropriate additives must be mixed into the adhesive. Thus, a corresponding mixing system is necessary. Furthermore the silicone-treated cover layer, upon application of the adhesive and during subsequent drying, is relatively strongly stressed. This stress is disadvantageous since the silicone layer which has been applied to the cover layer is generally very thin (up to roughly 1 micron) and damage to the silicone layer can easily occur even under low stresses. In this way, major problems can arise in a later detachment of the print carrier layer from the silicone-treated cover layer.
Furthermore, a process of the initially described type is known from practice; it is usually called the direct process. The direct process has been applied to date in print carrier layers made of PVC, the adhesive being applied to the PVC print carrier layer. After applying the adhesive, the layer material is sent to a drying station. When the adhesive on the PVC print carrier layer is dried, the temperature of the print carrier layer is only controlled by means of air temperature. The problem is that, in the direct process, plastic deformation and damage to the print carrier layer can occur when the allowable temperatures of the print carrier layer are not maintained.
The difference between the transfer process and the direct process is therefore that the adhesive in the transfer process is applied to the cover layer, while in the direct process the adhesive is applied to the print carrier layer. One advantage of the direct process is that the cover layer, and the silicone layer which is generally provided on the cover layer, are not unnecessarily stressed, as is the case in the transfer process. Therefore, damage to the silicone layer cannot occur. Another advantage of the direct process arises by the adhesive no longer being applied to an adhesive-repellant layer, but to the print carrier layer, and as a result, basically no additives need be added to the adhesive to preclude wetting faults. However, in the direct process, there is the danger of damage to the print carrier layer during heat treatment in the course of drying.
SUMMARY OF THE INVENTION
The primary object of this invention is to provide a process for producing a film sheet which can be carried out easily and economically, and with which damage to the print carrier layer is prevented during drying.
A second object of the invention is also to provide an apparatus for carrying out the aforementioned process.
The process in accordance with the invention, in which the aforementioned object is achieved, is characterized essentially in that the temperature of the print carrier layer provided with the adhesive layer is controlled. In the invention, the adhesive layer is applied to the print carrier layer and the print carrier layer provided with the adhesive layer is sent for drying. Here, the actual temperature of the print carrier layer provided with the adhesive layer is measured during drying. Depending on the measured current temperature of the print carrier layer provided with the adhesive layer, the drying temperature is adjusted to achieve a stipulated theoretical temperature of the print carrier layer. It should be pointed out in this connection that the adhesive layer need not be applied directly to the print carrier layer. The interposition of at least one other layer is easily possible, as is explained below.
In the implementation of the invention, it has been recognized that the print carrier layer which is provided with the adhesive layer can be damaged when the layer material assumes an overly high temperature during the drying process. For a faultless print carrier layer, drying in an exactly defined temperature range or at an exactly stipulated temperature is necessary. This drying which leads to neither plastic deformation nor other damage to the print carrier layer which is provided with the adhesive layer is accomplished in the invention by the fact that, in contrast to the known direct process, the temperature of the layer material comprising the adhesive layer and the print carrier layer is no longer controlled, but adjusted. Therefore, measurement of the current temperature of the print carrier layer which is provided with the adhesive layer and subsequent adjustments are done to achieve a certain set temperature of this layer material. In the invention, the temperature of the print carrier layer provided with the adhesive layer represents the controlled variable.
The process in accordance with the invention is especially suited for use with a material of the print carrier layer which is especially temperature sensitive. In this connection, especially polyolefins such as polypropylene, polybutene or polyethylene should be mentioned. These plastics are extremely sensitive to temperature and have a nonlinear temperature behavior. As soon as a certain critical temperature is reached or exceeded, a print carrier layer composed of this material is damaged. However, a print carrier layer of this plastic has good printability and durability. With the process according to the invention, for the first time, it is now possible to be able to use print carrier layers of polyolefins within the framework of the direct process without the danger of damage to this material during drying. In particular, when a plastic of this type is used as the material of the print carrier layer, the desired temperature is between 50° C and 70° C., and especially about 60° C. At this temperature, it is ensured that, on the one hand, prompt and good drying of the adhesive occurs, and on the other hand, that damage by plastic deformation of the print carrier layer is reliably prevented.
Although it would be fundamentally possible to measure the current temperature of the print carrier layer provided with the adhesive on the adhesive-free side via a sensor which has contact with this side, noncontact measurement of the temperature of the print carrier layer provided with adhesive is recommended. This precludes any loading by and onto the temperature sensors.
Otherwise, in addition to measuring the temperature of the print carrier layer provided with the adhesive, it is a good idea to provide another “regulator” to achieve a faultless film sheet. To do this, it is provided that, during drying, the tensile stress in the lengthwise direction of the print carrier layer provided with adhesive is measured and adjusted to a stipulated value. The tensile stress can be measured, fundamentally, even independently of the temperature control of the film sheet, i.e., even without temperature control of the film sheet. The tensile stress of
Crispino Richard
Jackstadt GmbH
Purvis Sue A.
Safran David S.
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